1. Field Of The Invention
The present invention is in the field of hydraulic accumulator devices and pertains more particularly to a low cost accumulator device having improved life cycle and seal characteristics.
2. The Prior Art
It is known to provide hydraulic systems with accumulator devices which generally comprise a pressure vessel interiorly divided into two chambers by an expansible and contractible bladder member of elastomic material or the like. The accumulator acts both as an energy storage device and as a pulsation dampener.
The gas chamber is charged with gas under pressure. When the pressure of the hydraulic system exceeds that of the gas chamber separated from the hydraulic system by the bladder, oil enters the vessel, causing the gas entrapped by the bladder to be compressed and deforming the bladder. When the pressure in the hydraulic system drops below that of the gas compressed within the bladder, hydraulic fluid is forced outwardly from the accumulator and, thus, the stored energy is returned to the system.
Heretofore accumulator devices of the type described have been quite costly, being formed of forged or machined pressure vessels having welded and/or other complex sealing arrangements for integrating the parts, elements or components of the accumulator.
There exists a substantial market for accumulator devices which may be fabricated at lower cost. Attempts have been made to provide low cost accumulators. One such device, which is more particularly described in pending U.S. application Ser. No. 305,522, filed Sept. 24, 1981, now U.S. Pat. No. 4,364,416 represents an attempt to reduce the cost of the accumulator by employing, in lieu of a forged or cast pressure vessel, a hydraulically formed, relatively thin walled spherical metal member. The device of the noted application includes a bladder member clampingly mounted between an output connection fixture intended to be coupled to the hydraulic system and the pressure vessel proper.
The subject device, while commercially acceptable, has been accompanied by a somewhat higher bladder failure rate and incidence of leakage than is desirable.
I have discovered that the bladder failure is attributable, in a measure, to the uncontrolled and rapid expansion and contraction of the bladder, which results in unequal stressing of the bladder components. As a result of such unequal stressing as, for example, may be experienced when a sudden and great surge of fluid is forced into the interior of the bladder, the bladder is deformed in an unpredictable manner.
In the course of such expansion, certain areas of the bladder may be stretched to a far greater degree than others causing a permanent set and consequent overlapping of areas of bladder with resulting cracking. The condition noted produces a progressive deterioration of the bladder since an area, once over-stressed, will be weakened, and subsequent pulses of hydraulic input are more likely to re-stress the previously weakened areas.